JPH01133011A - Optical fiber with synthetic resin coating and manufacture thereof - Google Patents

Abstract

PURPOSE: To prevent optical transmission loss arising from microbending by specifying the thickness of the first layer and modulus of elasticity of the second layer of an optical fiber having a synthetic resin coating consisting of the first sheath layer of synthetic rubber and the next synthetic resin sheath layer having the modulus of elasticity larger than the modulus of elasticity of the first layer. CONSTITUTION: A glass fiber 1 is provided with a soft buffer layer 2 consisting of the synthetic rubber having the modulus of elasticity of 0.1 to 10MPa right after the formation of this glass fiber. The first layer 2 is provided thereon with the solid upper layer 3 consisting of the second synthetic resin having the modulus of elasticity larger than the modulus of elasticity of the first layer in order to protect the soft buffer layer 2 during the execution of another treatment. The thickness of the first layer 2 is specified to 5 to 20μm and the modulus of elasticity of the second layer 3 to >=1000MPa. The modulus of elasticity of the second layer which exhibits a high value has an advantage in the mechanical resistance force of the optical fiber. As a result, the optical transmission loss occurring in the microbending is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber provided with a synthetic resin coating, including a glass fiber, a first outer skin layer of synthetic rubber having an elastic modulus of 0.1 to 10 MPa, and an elastic modulus greater than that of the first layer. It consists of the following synthetic resin outer skin layer:

Furthermore, the present invention relates to a method of manufacturing a curved optical fiber.

Glass fibers for optical telecommunications are generally coated with a synthetic resin coating to avoid mechanical damage. Coatings consisting of various layers are preferred to avoid optical transmission losses caused by microbending. For example, the following method is used. For example, immediately after forming a glass fiber by drawing from a preform or by using a double crucible method, a soft buffer layer of synthetic rubber having an elastic modulus of 0.1 to 10 MPa is applied. To protect the soft buffer layer during other treatments, the optical fiber is coated with a hard top layer of a second synthetic resin with an elastic modulus of more than 100 MPa.
r) on top of the 1N. Such a top layer is also applied immediately after forming the glass fiber, i.e. before winding the fiber onto a guide wheel or storing it. The buffer layer and the top layer together form the first synthetic resin coating of the glass fiber. Typical values for the diameter of the glass fiber with the first synthetic resin coating are 250 μm and the diameter of the glass fiber is 125 μm.

To protect the optical fiber from environmental influences during cabling, during cable laying, and during the life of the cable, optical fibers are often coated with a thicker second composite with a greater modulus of elasticity of I GPa. A resin coating is further provided. Such a second synthetic resin coating need not be applied immediately after forming the glass fiber.

Two examples of such second synthetic resin coatings are used. In a third example, an optical fiber provided with a first synthetic resin coating is placed at a distance with a second synthetic resin coating forming a tube. The gap between the optical fiber and the tube is filled with a thixotropic liquid or gel, such as silicone oil filled with extremely fine quartz particles. It is also possible to house one or more optical fibers within the tube. In another example, the second synthetic resin coating is adhesively bonded to the first synthetic resin coating.

In European patent application EP 155 051, an optical fiber is disclosed with a synthetic resin coating formed from a curable synthetic resin composition that is cured by exposure to radiation. The first synthetic resin coating consists of two layers, each having an elastic modulus of 0.1-10 MPa and 100 MPa. Both layers each have a thickness of approximately 30 μm.

It is an object of the invention to provide an optical fiber that is insensitive to internal mechanical influences, such as lateral forces on the fiber. The fiber must also be extremely insensitive to microbending, and the mechanical and optical properties should be as temperature-independent as possible during the processing temperatures of the fiber (-60 to +80 °C). It won't happen. Furthermore, it would be desirable to provide an optical fiber in which the second synthetic resin coating can be omitted.

The object of the present invention is achieved by the optical fiber described in the preamble, in which the thickness of the first layer is 5 to 20 μm and the modulus of elasticity of the second layer is 1.
It is characterized by a pressure of 000 MPa or more.

The elastic modulus values are measured at room temperature.

The high elastic modulus of the second layer is advantageous for the mechanical resistance of the optical fiber. Another advantage is that materials with high elastic moduli have high glass transition temperatures, which are beyond the range of optical fibers.

This helps reduce the temperature dependence of the optical fiber. The practical upper limit of the elastic modulus of filler-free isotropic synthetic resins is 3000 MPa. Fillers are undesirable because the filler particles exert local pressure on the optical fiber, which leads to transmission losses.

High modulus values are generally e.g.
/'C with a low value of linear thermal expansion coefficient. The corresponding value for quartz glass is 5X10-'/'C and for the material of the soft buffer layer is 5-40X10-'/'C. In the tube that cools the fiber, for example after manufacturing the fiber or during use of the fiber, large differences between the coefficients of linear thermal expansion of the fused silica and the coating can lead to axial bends in the optical fiber. This presents a transmission loss. Furthermore, the difference between the expansion coefficients of the top layer and the buffer layer in the radial direction presents bonding problems between the optical fiber and the soft buffer layer. However, in general, the linear expansion coefficient of synthetic resin coating is
Larger than that of optical fibers made from materials such as fused silica, the shrinkage of the buffer layer is much faster than the top layer, allowing the buffer layer to be separated from the fiber.

The invention is based on the finding that the problems caused by the use of very hard materials in the upper layer can be overcome by choosing the thickness of the first soft layer to be modest. A thin first layer provides sufficient protection, but unlike a thicker layer, it is constantly subjected to compressive pressure and cannot be separated from the optical fiber by shrinkage. Additionally, bending of optical fibers caused by temperature changes to some extent prevents transmission losses caused by bending from being reduced.

The provision of a thin first layer, which must be placed precisely concentrically around the optical fiber, is a difficult process to control. A method for measuring and controlling the installation of such thin layers is disclosed in Dutch Patent Application No. 8701346.

The thickness of the hard top layer is hardly critical, and the total diameter of the optical fiber with synthetic resin coating is approximately 250 mm.
Preferably, it is selected to be .mu.m. The diameter of quartz glass fibers is typically 125 μm, which means that the thickness of the top layer is between 40 and 60 μm. 2 of the fiber with a large thickness of the top layer, e.g.
An overall diameter greater than 50 μm results in large forces that cause bending in the fiber due to temperature changes.

The method of manufacturing the optical fiber of the present invention is such that both layers are formed from a curable synthetic resin composition, which is applied immediately after the optical fiber is drawn and cured by exposure to UV light or electrons. is preferred. The fiber of the present invention can be selectively manufactured by using a thermosetting synthetic resin composition. The problem of providing a hard layer of unfilled synthetic resin is solved by forming the second N from a curable resin composition containing ethoxylated bisphenol-A diacrylate, isocyanurate triacrylate, and less (both polyurethane acrylate). .

In a preferred embodiment of the invention, the first soft layer is molded from a curable synthetic resin composition containing polyether urethane acrylate. - Synthetic resin compositions suitable for use in the production of buffer layers are disclosed in European patent application EP 167199.

The curable synthetic resin compositions used for the manufacture of the buffer layer and the top layer can also contain other ingredients, such as monomeric acrylate compounds, which speed up the curing rate and reduce the viscosity. Appropriate additions include photosensitive initiators, catalysts and surface-active substances when curing is carried out by irradiation with UV light.

European Patent Application No. 213,680 discloses an optical fiber whose coating includes a portion of a material exhibiting a high modulus of elasticity in a predetermined preferred direction. In the radial direction, the elastic modulus is 600 MPa. Such materials can be used in the second and first synthetic resin coatings.

The thickness of the soft buffer layer is 30 μm.

U.S. Pat. No. 3,980,390 discloses coating with a 5-10 μm thick layer of thermally cured synthetic resin, followed by multiple layers of thermoplastic material, such as polythene or nylon, to a total thickness of 50 μm. Optical fibers applied by melt extrusion to have a diameter of ˜200 μm are disclosed. Such materials are considered unsuitable for producing strong optical fibers that are insensitive to ambient influences such as temperature and humidity.

The present invention will be explained by the following examples and comparative examples with reference to the drawings.

A one-sided dish multimode glass fiber was formed by drawing from a preform using known methods. It should be noted that glass fiber here means a fiber of glass or quartz glass. The fiber is made of core glass and Talarad glass (not shown in Figure 1) with different refractive indices.
including. Alternatively, the fiber may have a refractive index that gradually changes from the inside to the outside, and the double crucible method can be used instead of drawing the fiber from a preform.
) can also be used. The glass fiber 1 shown in Fig. 1 has a circular cross section (diameter 125 μm).
, but the cross section may have other shapes.

Immediately after forming the glass fiber 1, a layer of a curable synthetic resin composition is applied and then cured, thereby forming a thickness of 11 μm.
A synthetic rubber buffer layer of m was formed.

A method for applying thin layers to optical fibers is described in U.S. Pat. No. 4,644,899.
It is disclosed in Specification No. 8.

The curable synthetic resin composition is disclosed in European Patent Application No. 167199.
The curable synthetic resin composition, which contains polyether urethane acrylate represented by the following formula (n in the formula represents an average value of 120) as a main component (68% by weight) as disclosed in No. Reactive monomers 2-phenoxy-ethyl proacrylate (6% by weight) represented by the formula, tripylene glycol diacrylate (6% by weight) represented by the following formula, photosensitive initiator 2.2- Contains dimethoxy-2-phenyl-acetophenone (2% by weight) and p-chlorobenzophenone-2-ethoxy-ethyl acrylate (2% by weight) represented by the following formula.

The curable synthetic resin composition also contains 2% by weight of a mixture of mono- and di-2-acryloylethoxyphosphate in a molar ratio of 1:1 as shown in the following formula. The synthetic resin composition is also suitable for use in the buffer layer of the synthetic resin coating of the glass fiber of the present invention.

The curable synthetic resin composition is cured by irradiating it with a high-pressure mercury discharge lamp. Cough lamps emit UV light with a wavelength of 200-400 no+ and an intensity of 0.27 w/cm'' for a maximum of 0.5 seconds measured at the synthetic resin layer.Curable synthetic resin composition can be cured by other methods, for example by exposure to electron radiation, in which the curable synthetic resin composition does not need to contain a photosensitive initiator, after curing the elastic modulus of the material of the buffer layer was 1.3 MPa at room temperature.

The refractive index was 1.4808. The coefficient of linear expansion is -5°C
23xlO-'/'c at temperatures exceeding -60'C
It decreased as the temperature decreased to 10 × 10-'/'C.

Next, the fiber is coated with a curable synthetic resin composition and U
Synthetic resin 3 is cured by exposing it to V light.
A second layer of 52 μm thick was applied to the fiber. The synthetic resin layer suitable for the second N<the upper layer of the first synthetic resin coating includes a polyester urethane acrylate 19.1 represented by the following formula.
Weight %, isocyanurate triacrylate of the following formula: 23.9
4.5% by weight of 2,2-dimethoxy-2-phenyl-acetophenone represented by the following formula, and 52.5% by weight of ethoxylated bisphenol A diacrylate represented by the following formula. After curing, the modulus of such material is 1995 MPa at -60"C and 15 at +20"C.
It was 501 MPa at 85 MPa and +80°C.

The refractive index was 1.5279 at 20°C. The glass transition temperature Tg was about 100°C. The coefficient of linear expansion is -5
5X10-5/'C at a temperature lower than 'C and 80°
It increased with increasing temperature up to a value of 18X10-5/''C.

The optical fiber thus manufactured, in this example a multimode fiber, was subjected to a number of tests to measure transmission loss.

The compression test was performed by applying a clamping force of 50 KPa between a piece of fiber having a length of 0.5 m between two flat plates.
I held it in place (B force). One of the two plates had twelve grooves with sharp edges. Under these conditions and at a wavelength of light of 850 nm, the fiber according to the example is 0.38 dB at -60 °C, +20
Under unstressed conditions, the transmission loss caused by changes in temperature and tension at -60°C compared to room temperature showed a loss increase of 0.19 dB at +80°C and 0.18 dB at +80°C.
less than 0.2 dB/km at 55°C and 0.056B/km at +80°C.

An optical fiber was manufactured and coated in the same manner as described in Example 1, except that a single mode fiber was used. The thickness of the buffer layer is 12 or 19 μm, respectively, and the thickness of the upper layer is 5 μm.
It was 0 or 43 μm.

Under unstressed conditions, the transmission loss caused by changes in temperature and tension is 13.00 compared to room temperature.
Measured at the wavelength of light of nm - 0 at 60°C and 80°C
．． It was 0 dB/km.

The strength of the optical fiber before being subjected to a lateral force is set to a diameter of 0.
Measurements were made by winding 150 m of optical fiber into a 5 m cylinder. The cylinder is covered with sandpaper (No.
120). The winding force was 2N.

The increase in transmission loss as a result of such treatment is 1300n
m and 0.1 dB/km at a wavelength of light of 1500 nm,
It was 0.6 dB/km at 1700 nm, and the buffer layer thicknesses were both 12 nm and 19 nm.

An optical fiber was produced and coated in the same manner as described in Example 1, except that the thickness of the buffer layer was 8 μm and the thickness of the upper layer was 55 μm. The upper layer consists of 10% by weight of polyester urethane acrylate represented by the following formula, 18% by weight of isocyanurate triacrylate represented by the following formula', 10% by weight of epoxy acrylate represented by the following formula, and 10% by weight of epoxy acrylate represented by the following formula) I
A curable synthetic resin composition was prepared from 4% by weight of 1-hydroxycyclohexylphenylketone represented by n and 58% by weight of ethoxylate bisphenol-A diacrylate represented by the following formula. After curing, the elastic modulus of such material is 1420 at room temperature.
It was MPa.

A single mode optical fiber was manufactured by the method described in Example 1, except that the Tonko-Goto buffer layer was not applied.

Under stress-free conditions, the transmission loss caused by temperature changes was 0.0 dB/km at -60°C and 80°C, measured at a wavelength of light of 1300 nm, compared to room temperature.

Transverse load sensitivity (transverse-1oad 5
sensitivity) was measured by the emery paper test. The increase in transmission loss is 1. at a wavelength of 1300 nm. ．．
3 dB/km, 2.0 dB/k at 1550 nm
m and 3.1 dB/km at 1700 nm.

In this comparative example, the temperature sensitivity (tempa
5 sensitivity) is small, but
The lateral load sensitivity is large and undesirable.

A single-layer multimode fiber was prepared as described in Example 1. The thickness of the buffer layer was 27 or 35 μm and the thickness of the top layer was 36 or 27 μm, respectively.

When a fiber with a 35 μm buffer layer is subjected to the compression test described in Example 1, the transmission loss is 0.05 d at room temperature.
In B, the wavelength of light was 850 nm.

Under stress-free conditions, the transmission loss caused by temperature changes is -35 μm buffer at 1.0 dB/km for an optical fiber with a 27 μm buffer layer at -60°C and a wavelength of light of 850 nm compared to room temperature. For fibers with layers, it was greater than 10 dB/Km. Furthermore, both fibers have a temperature of 0.05 at +80'C.
It had a transmission loss of less than dB/km.

Although the load resistance is small, the fiber of this comparative example is sensitive to temperature changes,
In particular, it is undesirably highly sensitive to cooling.

This single-mode fiber was manufactured by the method described in Example 1. The thickness of the buffer layer was 24 or 33 μm, respectively, and the thickness of the top layer was 39 or 30 μm.

The lateral load sensitivity of the fiber with a 33 μm buffer layer was measured with emery paper. The increase in transmission loss was less than 0.05 dB/km at wavelengths of light of 1300 or 1550 nm, and 0.1 dB/km at 1700 nm.

Under unstressed conditions, the transmission loss caused by temperature changes is 0.8 dB/km compared to room temperature for a fiber with a 24 μm buffer layer at wavelengths of light of -60 °C and 1300 nm for a 33 μm buffer layer. was greater than 4 dB/km for fibers with .

Although the load resistance is small, the fiber of this comparative example is sensitive to temperature changes,
In particular, it is undesirably highly sensitive to cooling.

A static multimode fiber was manufactured as described in Example 1. The thickness of the buffer layer was 33 μm, and the thickness of the top layer was 32 μm. A commercially available synthetic resin composition for the buffer layer is Desolite (Deso) manufactured by Desoto.
1 ite) 039■, and the upper layer was manufactured from Desolite 042■ manufactured by DEAD. Both synthetic resin compositions contain a photosensitive initiator. After curing, the elastic modulus of Desolite 042■ is 1585 MPa at -60°C.
398 MPa at +20°C and 13 MPa at +80°C
It was a.

Under stress-free conditions, the transmission loss caused by temperature changes is 0.1 dB/km at -60°C and 0.0 at +80°C at a wavelength of 850 nm light compared to room temperature.
It was smaller than 5dB/km.

In the compression test described in Example 1, at a wavelength of light of 850 nm, the transmission loss was 0.69 dB at -60°C, +
0.21dB at 20°C and 0.37dB at +80°C
Met. The fiber of this comparative example is quite sensitive to mechanical loading (undesirable).

A comparative single mode optical fiber was manufactured from the synthetic resin composition described in Comparative Example 6. The thickness of the buffer layer was 32 μm and the thickness of the top layer was 33 μm.

Under stress-free conditions, the transmission loss caused by temperature changes is less than 0.05 dB/km at -60"C and +80"C at a wavelength of 1300nm light compared to room temperature.
It was 0.0 dB/km.

The lateral load sensitivity of the optical fiber is measured using sandpaper (abrsiν
epapen) test. The increase in transmission loss is 1.3 dB/km at a wavelength of 1300 nm,
2.7 dB/km at 1550nm, 1700nm
It was 5.5 dB/km. The fiber of this comparative example was extremely sensitive to lateral loads.

Optical fibers with high resistance to mechanical loads and high insensitivity to temperature changes use synthetic resin coatings consisting of an upper layer with a high elastic modulus and a soft buffer layer that must be thin but must be present. It is clear from the above example that this can only be obtained by The critical thickness depends on the differential thermal expansion between the buffer layer and the top layer and must not be exceeded.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the optical fiber of the present invention. 1... Glass fiber 2... Buffer layer 3... Second synthetic resin layer

Claims (1)

[Claims] 1. A synthetic resin coating consisting of a glass fiber, a first outer skin layer of synthetic rubber having an elastic modulus of 0.1 to 10 MPa, and a next synthetic resin outer skin layer having an elastic modulus greater than that of the first layer. In the optical fiber provided, the thickness of the first layer is 5~
An optical fiber provided with a synthetic resin coating, characterized in that the elastic modulus of the second layer is 1000 MPa or more at 20 μm. 2. In manufacturing the fiber according to claim 1, both layers are formed from a curable synthetic resin composition, which is applied immediately after drawing the optical fiber and cured by exposure to UV light or electrons. A method for manufacturing an optical fiber with a synthetic resin coating, characterized in that: 3. The method of claim 2, wherein the second hard layer is formed from a curable resin composition comprising an ethoxylated bisphenol-A diacrylate, an isocyanurate triacrylate, and at least a polyurethane acrylate. 4. The method according to claim 2, wherein the first soft layer is formed from a curable synthetic resin composition containing at least one type of polyether urethane acrylate.